.TH std::future::valid 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::future::valid \- std::future::valid

.SH Synopsis
   bool valid() const noexcept;  \fI(since C++11)\fP

   Checks if the future refers to a shared state.

   This is the case only for futures that were not default-constructed or moved from
   (i.e. returned by std::promise::get_future(), std::packaged_task::get_future() or
   std::async()) until the first time get() or share() is called.

   The behavior is undefined if any member function other than the destructor, the
   move-assignment operator, or valid is called on a future that does not refer to
   shared state (although implementations are encouraged to throw std::future_error
   indicating no_state in this case). It is valid to move from a future object for
   which valid() is false.

.SH Parameters

   \fI(none)\fP

.SH Return value

   true if *this refers to a shared state, otherwise false.

.SH Example


// Run this code

 #include <future>
 #include <iostream>

 int main()
 {
     std::promise<void> p;
     std::future<void> f = p.get_future();

     std::cout << std::boolalpha;

     std::cout << f.valid() << '\\n';
     p.set_value();
     std::cout << f.valid() << '\\n';
     f.get();
     std::cout << f.valid() << '\\n';
 }

.SH Output:

 true
 true
 false

.SH See also

   wait waits for the result to become available
        \fI(public member function)\fP
